1. Field of the Invention
The present invention relates to an IC socket which comprises a socket body, a cover and a plurality of contacts and allows engagement and disengagement of said contacts with the leads of the IC package by vertical movement of said cover, and, more specifically, an improvement in the operation and engagement of the contacts with the IC package.
2. Description of the Prior Art
Generally, all IC packages are subject to screening inspections by several methods to ensure their original functions. One of these screening inspections of the IC packages is a burn-in test, which is intended to test high temperature characteristics of IC packages by setting the IC packages mounted on IC sockets in a convective oven and actuating them in a high temperature environment.
For use in the above described burn-in tests, several IC sockets adapted to inspections by automatic machines have bene applied. For example, the IC sockets applicable to automatic machines have been disclosed in the Unexamined Patent Publication 1987-160676, Unexamined Patent Publication 1988-62175, Unexamined Patent Publication 1988-299257, Unexamined Patent Publication 1990-94347, U.S. Pat. No. 4,623,208 and U.S. Pat. No. 4,886,470.
FIGS. 15 to 20 respectively show the IC sockets disclosed in the above documents. More specifically, FIG. 15 is a cross-sectional view of the conventional IC socket disclosed in the Unexamined Patent Publication 1987-160676, FIG. 16 is a cross-sectional view of the conventional IC socket disclosed in the Unexamined Patent Publication 1988-62175, FIG. 17 is a cross-sectional view of the conventional IC socket disclosed in the Unexamined Patent Publication 1988-299257, FIG. 18 is a cross-sectional view of the conventional IC socket disclosed in the Unexamined Patent Publication 1990-94374, FIG. 19 is a cross-sectional view of the conventional IC socket disclosed in the U.S. Pat. No. 4,623,208 and FIG. 20 is a cross-sectional view of the conventional IC socket disclose din the U.S. Pat. No. 4,886,470.
These IC sockets respectively comprise a socket body 1', cover 2' and a plurality of contacts 3'. The contacts 3' respectively have a contact portion 34' for leads of the IC package, a circular-curved cantilever portion 32' and an engaging portion 35' for the cover. When the cover 2' is pushed down against a repulsive force of the contacts, these contacts 3' are displaced outwardly and released from engagement with the leads of the IC package. Under this condition, therefore, the IC package can be remounted. When the cover 2' is released from pushing force, the contacts 3' are rotated in the opposite direction and re-engaged with the leads of the IC package.
However, these IC sockets of the prior art have the problems as described below since the opening of the circular-curved cantilever portion 32' of the contact is faced outwardly and the contact is displaced mainly by a resilient profiled portion.
Specifically, the connecting portion 36', where the contact portion 34' and the engaging portion 35' are branched from the cantilever portion 32', is moved down when operated and therefore the amount of movement of the contact portion in a direction where the contact portion 34' moves away from the IC package is small, the IC package can be mounted or demounted, and the leads of the IC package curve during remounting operation.
An internal stress of the contacts 3' is concentrated partially in operation and the spring characteristic of the contacts cannot be maintained for a long period of time.
A force of engagement of the contacts and the leads is obtained as a resilient repulsive force, by which the contacts are displaced as much as the thickness of the leads of the IC package, and therefore, the engaging force has been substantially affected in accordance with the variations in the thickness of leads when IC packages having different thicknesses of IC package leads and a stable engaging force could not be obtained.
In addition, the engaging portion 21' of the cover 2' for the contacts 3' has been formed as a horizontal surface or a single inclined surface and therefore there has been no variation of the depressing force of the cover 2' during depressing operation and the lowest position of downward movement could not actually be known. Accordingly, the cover has been further pushed down even when it is at the lowest position and the IC socket and the board have been damaged in some cases.
In view of the above-described actualities, an object of the present invention is to provide an IC socket, including the contacts, capable of facilitating the remounting of the IC package and guaranteeing the reliability of engagement with the IC package for a long period of time.
Another object of the present invention is to provide an IC socket including the contacts, which are hardly affected by variations in the thickness of leads of the IC package and are able to provide a stable engaging force.
Another object of the present invention is to provide an IC socket adapted to change a depressing force at a specified position before the lowest position of downward movement, and to know in advance the lowest position when the cover is operated.